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cervical length and risk of spontaneous preterm delivery

Dr Françoise Dupont

Hm-envelop

Pr Pierre Durand

Hm-envelop
OVERVIEW

Spontaneous preterm birth (sPTB) remains one of the most significant challenges in modern obstetrics and is a leading cause of neonatal morbidity and mortality worldwide. Despite advances in perinatal and neonatal care, the overall incidence of preterm birth has not declined substantially over recent decades. A central feature in the pathophysiology of spontaneous preterm delivery is premature cervical remodeling, which manifests clinically as cervical shortening, softening, and dilatation prior to the onset of labor. Among the various tools available to assess this process, transvaginal ultrasonographic measurement of cervical length has emerged as the most robust and reproducible predictor of spontaneous preterm delivery. The relationship between cervical length and preterm birth risk, and the therapeutic implications of identifying a short cervix, constitute the foundation of contemporary prevention strategies.

The cervix plays a critical mechanical and biological role in maintaining pregnancy. Under normal circumstances, cervical remodeling is a gradual, tightly regulated process that occurs late in gestation, allowing for term labor. In spontaneous preterm birth, this remodeling occurs prematurely and independently of overt uterine contractions in many cases. The concept of the preterm parturition syndrome frames preterm birth as a final common pathway resulting from heterogeneous processes—infectious, inflammatory, endocrine, mechanical, or vascular—that converge on cervical change.

Cervical shortening detected in the mid-trimester is therefore not merely an anatomic finding but a surrogate marker of these underlying pathological processes. Importantly, shortening may precede clinical symptoms by weeks, providing a critical window for risk stratification and intervention.

Transvaginal ultrasound (TVUS) is the gold standard for cervical length assessment. Compared with digital examination, TVUS offers superior objectivity, reproducibility, and predictive accuracy. Large prospective studies have demonstrated that cervical length follows a roughly normal distribution in mid-pregnancy, with mean values around 35 mm at 24 weeks’ gestation. As cervical length decreases, the risk of spontaneous preterm delivery increases in a continuous and inverse relationship, rather than at a single pathological threshold.

Landmark multicenter studies have shown that women with a cervical length below the 10th percentile—and particularly below 25 mm—are at markedly increased risk of delivery before 34 or 35 weeks. This risk escalates dramatically as cervical length shortens further, reaching its highest levels in women with measurements below 15 mm. These findings apply to both low-risk women and those with prior obstetric risk factors, although absolute risk is greatest when a short cervix is combined with a history of spontaneous preterm birth.

The predictive value of cervical length measurement is greatest when performed in the mid-trimester, typically between 16 and 24 weeks of gestation. Before 16 weeks, cervical measurements have limited predictive utility, while after 24 weeks the opportunity for preventive interventions diminishes. Current evidence supports targeted screening in women with prior spontaneous preterm birth, but there is increasing support for universal cervical length screening in singleton pregnancies, given the effectiveness and safety of available interventions.

In multiple gestations, particularly twin pregnancies, cervical shortening is common and strongly associated with preterm birth. However, management strategies differ, as some interventions effective in singleton pregnancies—such as cerclage—may be ineffective or even harmful in twins.

Identification of a short cervix has clinical value only if effective interventions exist. Historically, management strategies such as bed rest, activity restriction, prolonged tocolysis, or antibiotics were widely used despite poor evidence of benefit. High-quality trials have since clarified the roles of progesterone therapy and cervical cerclage, while refuting many older practices.

Vaginal progesterone has emerged as one of the most important preventive therapies for women with a sonographically short cervix. Randomized controlled trials have demonstrated that, in asymptomatic women with singleton pregnancies and a cervical length typically ≤15–25 mm, vaginal progesterone significantly reduces the rate of spontaneous preterm birth before 33–34 weeks and improves neonatal outcomes. Importantly, this benefit appears consistent regardless of whether the woman has a prior history of preterm birth.

Progesterone is thought to exert its effects through multiple mechanisms, including suppression of inflammatory pathways, reduction of cervical ripening, and maintenance of uterine quiescence. Its favorable safety profile and ease of administration have strengthened the argument for universal mid-trimester cervical length screening.

Cervical cerclage is a surgical intervention aimed at mechanically reinforcing the cervix. Evidence indicates that cerclage is beneficial primarily in a highly selected subgroup: women with a singleton pregnancy, a history of spontaneous preterm birth, and a short cervix detected in the mid-trimester. In contrast, cerclage has not demonstrated benefit in women without prior preterm birth and may increase adverse outcomes in twin pregnancies.

These findings underscore the importance of individualized risk stratification rather than a uniform intervention strategy.

Although cervical length is a strong predictor of outcome, studies evaluating the utility of repeat measurements, particularly after interventions such as tocolysis for threatened preterm labor, have shown limited additional predictive value. Once a short cervix is identified, its prognostic significance appears to be driven more by the absolute measurement than by short-term changes.

This has shifted focus toward earlier identification rather than intensive serial monitoring in symptomatic settings.

While cervical length measurement is currently the cornerstone of prediction, it captures only the geometric aspect of cervical remodeling. Novel techniques, such as shear wave elastography, aim to assess cervical stiffness and biomechanical properties, potentially detecting preclinical changes before shortening occurs. Early feasibility studies suggest that cervical softening may be independently associated with preterm birth risk, but these techniques remain investigational and are not yet integrated into routine practice.

Cervical length assessment by transvaginal ultrasound represents one of the most powerful tools in obstetrics for predicting spontaneous preterm delivery. The inverse relationship between cervical length and preterm birth risk is robust, continuous, and clinically actionable. Identification of a short cervix enables targeted, evidence-based interventions—most notably vaginal progesterone and, in selected cases, cervical cerclage—that significantly reduce preterm birth and improve neonatal outcomes. Ongoing research into cervical biomechanics and universal screening strategies continues to refine this paradigm, positioning cervical assessment as a cornerstone of modern preventive obstetrics.

FAQ

The cervix maintains pregnancy by remaining long, firm, and closed until late gestation. Premature cervical remodeling compromises this function and increases the risk of early delivery.

Cervical remodeling refers to biochemical and structural changes—shortening, softening, and dilatation—that normally occur near term but may occur prematurely in sPTB.

Cervical length is best measured by transvaginal ultrasound, which provides superior accuracy and reproducibility compared with digital examination or transabdominal approaches.

Measurement between 16 and 24 weeks of gestation provides the highest predictive value for spontaneous preterm birth.

A cervical length of ≤25 mm in the mid-trimester is commonly used as the threshold for increased risk, although risk rises continuously as length decreases.

Yes. The risk of sPTB increases progressively as cervical length shortens, rather than abruptly at a single cutoff value.

Yes. Even in women without prior obstetric risk factors, a short cervix is a strong independent predictor of spontaneous preterm birth.

Women with both a prior spontaneous preterm birth and a short cervix have the highest absolute risk of recurrence.

No. Digital examination is subjective and poorly predictive compared with transvaginal ultrasound measurement.

Vaginal progesterone significantly reduces the risk of spontaneous preterm birth and neonatal morbidity in women with a singleton pregnancy and a short cervix.

Yes. Evidence shows that vaginal progesterone is effective in asymptomatic women with a short cervix regardless of prior obstetric history.

Progesterone helps maintain uterine quiescence, reduces cervical inflammation, and delays cervical remodeling.

Cerclage is beneficial mainly in women with a singleton pregnancy, a history of spontaneous preterm birth, and a short cervix detected in the mid-trimester.

No. In women without prior sPTB, cerclage has not been shown to reduce preterm birth and may increase complications.

Cerclage is generally ineffective and may be harmful in twin pregnancies, even when cervical shortening is present.

Repeat measurement after successful tocolysis does not improve prediction of preterm birth and has limited clinical utility.

Evidence suggests that universal screening combined with vaginal progesterone is effective, safe, and cost-saving in singleton pregnancies.

Yes. Techniques such as shear wave elastography aim to assess cervical stiffness, but they remain investigational and are not yet part of routine care.

DO'S AND DONTS

TVUS provides objective, reproducible, and validated measurements and is superior to digital, transabdominal, or transperineal approaches for predicting spontaneous preterm birth.

This gestational window offers the highest predictive accuracy and aligns with the timing used in intervention trials for progesterone and cerclage.

Preterm birth risk increases progressively as cervical length shortens; clinical thresholds (e.g. 25 mm) are pragmatic, not biological absolutes.

High-quality randomized trials demonstrate significant reductions in early preterm birth and neonatal morbidity with excellent safety profiles.

Cerclage should be reserved for women with a singleton pregnancy, prior spontaneous preterm birth, and a short cervix—where evidence supports benefit.

Relying solely on obstetric history misses many at-risk women; current-pregnancy cervical assessment is essential.

Probe pressure, bladder filling, and landmark identification significantly affect measurements; standardized protocols are critical.

A short cervix increases risk but does not guarantee preterm birth; progesterone reduces risk but does not eliminate it.

Predictive value and treatment efficacy differ substantially; evidence-based interventions for singletons cannot be extrapolated to twins.

Biomechanical assessment of the cervix is promising but currently complements research, not routine clinical decision-making.

Digital exams are subjective and consistently inferior to TVUS cervical length for risk stratification.

Screening is only justified when effective interventions (e.g. progesterone) are available and implemented appropriately.

Cervical shortening may result from diverse mechanisms (inflammatory, mechanical, endocrine) with different therapeutic implications.

Randomized trials show no benefit—and potential harm—when cerclage is applied broadly without appropriate selection.

Progesterone and cerclage have not shown consistent benefit in twin pregnancies with cervical shortening.

Repeat measurements over short intervals add little prognostic value once baseline cervical length is known.

Bed rest has no proven benefit and may increase maternal morbidity and psychosocial harm.

Cervical shortening often precedes contractions; prevention is most effective when applied before clinical preterm labor.

Predictive markers must be linked to interventions that improve outcomes, not merely identify risk.

In singleton pregnancies, failure to screen denies access to proven, low-risk preventive therapy.

BIBLIOGRAPHY
  1. Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Das A, et al.
    The length of the cervix and the risk of spontaneous premature delivery. New England Journal of Medicine. 1996;334(9):567–572.
  2. Rozenberg P, Rudant J, Chevret S, Boulogne AI, Ville Y.
    Repeat measurement of cervical length after successful tocolysis. Obstetrics & Gynecology. 2004;104:995–999.
  3. Fonseca EB, Celik E, Parra M, Singh M, Nicolaides KH.
    Progesterone and the risk of preterm birth among women with a short cervix. New England Journal of Medicine. 2007;357:462–469.
  4. Hassan SS, Romero R, Vidyadhari D, Fusey S, Baxter JK, Khandelwal M, et al.
    Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter randomized double-blind placebo-controlled trial. Ultrasound in Obstetrics & Gynecology. 2011;38(1):18–31.
  5. Combs CA.
    Vaginal progesterone for asymptomatic cervical shortening and the case for universal screening of cervical length. American Journal of Obstetrics and Gynecology. 2012;206:124–130. (Editorial)
  6. Campbell S.
    Universal cervical-length screening and vaginal progesterone prevents early preterm births, reduces neonatal morbidity and is cost saving: doing nothing is no longer an option. Ultrasound in Obstetrics & Gynecology. 2011;38:1–9. (Editorial)
  7. Berghella V, Odibo AO, Tolosa JE.
    Cerclage for prevention of preterm birth in women with a short cervix found on transvaginal ultrasound examination: a randomized trial. American Journal of Obstetrics and Gynecology. 2004;191:1311–1317.
  8. Vayssière C, Favre R, Audibert F, Chauvet MP, Gaucherand P, Tardif D, et al.
    Cervical assessment at 22 and 27 weeks for the prediction of spontaneous birth before 34 weeks in twin pregnancies: is transvaginal sonography more accurate than digital examination? Ultrasound in Obstetrics & Gynecology. 2005;26:707–712.
  9. Muller M, Aït-Belkacem D, Hessabi M, Gennisson JL, Grangé G, Goffinet F, et al.
    Assessment of the cervix in pregnant women using shear wave elastography: a feasibility study. Ultrasound in Medicine & Biology. 2015;41(11):2789–2797.
  • Reicher L, Fouks Y, Yogev Y.
    Cervical assessment for predicting preterm birth—cervical length and beyond. Journal of Clinical Medicine. 2021;10:627. (Narrative review)

Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Das A, et al.
The length of the cervix and the risk of spontaneous premature delivery. New England Journal of Medicine. 1996;334(9):567–572.

This NICHD Maternal–Fetal Medicine Units Network study aimed to evaluate whether transvaginal ultrasound (TVUS) cervical length—measured prospectively in asymptomatic women—could quantify risk of spontaneous delivery before 35 weeks, and whether that risk behaved as a threshold phenomenon or a continuum.

Objectives

  1. To measure cervical length by standardized TVUS at ~24 and ~28 weeks in singleton pregnancies.
  2. To determine the relationship between cervical length and spontaneous preterm delivery <35 weeks.
  3. To compare ultrasound measures (length, funneling) with digital examination (Bishop score), and explore clinically relevant cutoffs using ROC approaches.

Methods

Design and setting: Prospective, multicenter cohort study across 10 university-affiliated prenatal clinics.

Participants: 3073 enrolled; after exclusions, 2915 women underwent TVUS at ~24 weeks and 2531 had repeat assessment at ~28 weeks. Participants had singleton pregnancies and were outpatients without symptoms of preterm labor at the time of examination. Baseline demographics reflect a largely socioeconomically disadvantaged cohort (e.g., high proportion Black, low income, incomplete high school), and 16% reported a prior preterm delivery (<37 weeks), including spontaneous and medically indicated events.

Ultrasound technique and quality control: Digital cervical exam preceded ultrasound. For TVUS, operators obtained a sagittal view identifying key landmarks (echodensity at external os, V-shaped notch at internal os). To avoid artificially lengthening the cervix, probe pressure was minimized by withdrawing until blur and reapplying only minimal pressure. The cervix was measured three times along the endocervical canal; the shortest qualifying measurement was recorded (recognizing first measurements may be 3–5 mm longer due to probe pressure). Each exam lasted at least 3 minutes to allow identification of a funnel (membrane protrusion ≥3 mm into internal os) and to record funnel presence/length. Standardization included training materials, certification of sonographers, random quality-control tapes, and central review of all images by a single investigator blinded to outcomes.

Outcome: Primary outcome was spontaneous preterm delivery before 35 weeks (spontaneous labor/rupture of membranes, not medically indicated).

Statistical analysis: Cervical length treated as a continuous predictor and also categorized by percentiles. Relative risks (RRs) were computed by comparing women at/below given percentiles against those above the 75th percentile. Logistic regression, survival analysis, and ROC curves explored predictive performance. Correlation between cervical length and Bishop score was tested statistically.

Main results

Incidence of sPTB <35 weeks: Among those examined at 24 weeks, spontaneous delivery <35 weeks occurred in 126/2915 (4.3%); among those examined at 28 weeks, 83/2531 (3.3%) delivered spontaneously <35 weeks. Rates varied by center (1.5%–5.1%). A minority received parenteral tocolysis (3.1%), most delivering ≥35 weeks—illustrating that many “at-risk” presentations do not result in early delivery.

Distribution of cervical length: Cervical length was approximately normally distributed and decreased slightly from 24 to 28 weeks: mean 35.2 ± 8.3 mm at 24 weeks and 33.7 ± 8.5 mm at 28 weeks. Although nulliparous women had slightly shorter mean lengths than parous women, the differences were statistically significant but considered clinically small; parity strata were therefore combined.

Risk gradient across percentiles (key contribution): Risk rose progressively as cervical length shortened, even for lengths well above extreme “short cervix” cutoffs. Using women above the 75th percentile as reference, the RRs for sPTB <35 weeks at 24 weeks’ measurement were:

  • ≤75th percentile (≤40 mm): RR 1.98
  • ≤50th percentile (≤35 mm): RR 2.35
  • ≤25th percentile (≤30 mm): RR 3.79
  • ≤10th percentile (≤26 mm): RR 6.19
  • ≤5th percentile (≤22 mm): RR 9.49
  • ≤1st percentile (≤13 mm): RR 13.99
    with strong statistical significance for much of this gradient. At 28 weeks, corresponding RRs were even larger (2.80, 3.52, 5.39, 9.57, 13.88, 24.94).

Continuous model: Logistic regression suggested that for each 1 mm increase in cervical length, odds of preterm delivery decreased (odds ratio about 0.91 per mm). Crucially, the association was evident across the range; even women above the 10th percentile showed increasing risk as length decreased.

Change between 24 and 28 weeks: A decrease in length over time had a statistically significant but modest independent association with risk. Women whose cervix shortened between visits had a higher preterm delivery rate (4.2% vs 2.1%; RR ~2.03). A shortening of ≥6 mm conferred higher risk (RR ~2.80 compared with <6 mm change).

Funneling and Bishop score: Funneling was predictive but suffered major inter-center variability (e.g., 0% at one center vs 12.7% at another at 24 weeks), likely related to probe pressure and transducer differences. After controlling for center and cervical length, funneling still predicted outcome, but the authors emphasized that cervical length was more consistently measured and performed as well as or better than funneling. Cervical length correlated with Bishop score; those with Bishop ≥6 had shorter mean cervical lengths, yet the Bishop score’s overall clinical utility remained limited compared to TVUS length.

Interpretation and implications

This study reframed cervical competence as a continuum rather than a binary state: shorter cervix in mid-pregnancy corresponded to progressively higher sPTB risk. The findings argued against the idea that shortening simply reflects occult labor, citing outpatient asymptomatic status and survival curves showing divergence over time rather than immediately post-measurement. The work helped establish TVUS cervical length as a cornerstone of risk stratification and laid conceptual groundwork for later intervention trials (e.g., progesterone, selective cerclage).

Strengths and limitations

Strengths: large sample size; multicenter design; rigorous sonographer training and central blinded image review; robust statistical exploration including continuous and percentile-based models.
Limitations: inter-center variability in funneling detection; demographic composition may affect generalizability; observational design cannot prove causality; outcome focused on <35 weeks (clinically meaningful but different from <34/<32 thresholds used later).

Teaching takeaways

For learners, this paper is foundational for: (1) why TVUS cervical length is superior to digital exam; (2) how risk scales continuously with shortening; and (3) why a “short cervix” threshold (e.g., 25 mm) is a pragmatic clinical cutoff rather than a biological switch.

Rozenberg P, Rudant J, Chevret S, Boulogne AI, Ville Y.
Repeat measurement of cervical length after successful tocolysis. Obstetrics & Gynecology. 2004;104:995–999.

Transvaginal ultrasound (TVUS) cervical length (CL) had already emerged as a strong predictor of spontaneous preterm delivery in asymptomatic women, but its optimal role in symptomatic settings (PTL, tocolysis) was less clear. One pragmatic question was whether a repeat CL measurement after contractions have been suppressed (i.e., after “successful tocolysis”) adds useful prognostic information beyond the initial CL at admission. Rozenberg and colleagues designed this prospective study to test whether repeating CL before discharge improves prediction of preterm delivery relative to the baseline admission measurement.

Objectives

  1. To measure CL by TVUS at admission for PTL and again after successful tocolysisin women who remained undelivered.
  2. To determine whether the change (variation) in CLafter tocolysis improves prediction of preterm delivery, compared with CL measured before starting tocolysis.

Methods

Design: Prospective observational study.

Population and inclusion criteria: Women admitted for uterine contractions between 24+0 and 33+6 weeks’ gestation, with an admission TVUS CL of ≤26 mm. This inclusion criterion intentionally focused on women already considered at increased risk (short cervix) to see if serial measurement could refine risk further.

Clinical management and definition of “successful tocolysis”: Intravenous tocolysis was administered (details are described clinically in the paper context), and “successful tocolysis” was operationally defined as delivery delayed by at least 48 hours, after which intravenous tocolysis was stopped. Only women who remained undelivered and clinically stable proceeded to the second (“discharge”) CL measurement.

Cervical length assessments: CL was measured by TVUS at two time points: (1) on admission before or at the initiation of treatment for PTL, and (2) before discharge after cessation of tocolysis (i.e., after contractions were controlled and no delivery occurred within 48 hours). The study then computed the variation in CL (discharge CL minus admission CL), capturing both increases and decreases.

Outcome: Primary outcome was preterm delivery, defined as delivery before 37 weeks. (Notably, this outcome differs from studies focusing on <34 or <35 weeks; the authors chose the conventional <37 week definition to reflect broad clinical prematurity.)

Statistical approach: Predictive analyses were based on logistic regression models estimating odds ratios (ORs) and 95% confidence intervals (CIs). The key modeling question was whether adding the variation in CL to a model already including baseline CL improves prediction of preterm delivery. Models adjusted for clinically relevant confounders such as parity and gestational age at admission, alongside baseline CL.

Main results

Study sample: 109 patients were included. On admission, the median (1st, 3rd quartile) CL was 18 (13, 22) mm, confirming that the cohort represented a high-risk symptomatic population.

Change in cervical length after tocolysis: After successful tocolysis and cessation of IV medication, the median variation in CL was +3 (0, 8) mm, with a wide range from −13 to +26 mm. This variability is clinically intuitive: some cervixes may lengthen when uterine activity resolves and the lower uterine segment relaxes, while others may continue to shorten despite suppression of contractions. The key empirical point is that the distribution of change was broad enough that, if change truly carried prognostic value, the study should have been able to detect at least a trend.

Time to delivery and prematurity rate: The median interval from tocolysis to delivery was 53.0 (35.0, 70.0) days. Despite initial symptomatic PTL with short cervix, a substantial fraction still achieved later gestations. However, 45 women (41.3%) delivered before 37 weeks, indicating a high rate of preterm delivery consistent with the selected high-risk inclusion criterion (short CL ≤26 mm plus contractions).

Does the repeat measurement add predictive value? The central finding is negative: the variation in cervical length after successful tocolysis did not improve prediction of preterm delivery beyond baseline CL and clinical variables. After adjustment for baseline CL, parity, and gestational age at admission, the odds ratio associated with CL variation was 0.97 (95% CI 0.90–1.03; P = .27)—statistically non-significant and clinically small in magnitude. In other words, whether the cervix lengthened or shortened modestly after tocolysis did not meaningfully change the probability of delivering before 37 weeks once you already knew (a) how short the cervix was at presentation and (b) basic clinical context.

Interpretation

The authors conclude that repeating TVUS CL measurement after successful tocolysis is “useless” for improving prediction in this setting. The study implies that baseline cervical status at the time of symptomatic presentation captures most of the prognostic information available from CL in women with PTL and intact membranes who remain undelivered after 48 hours.

A clinically important nuance is what this does—and does not—mean. It does not deny that CL is prognostically meaningful in PTL; rather, it suggests that the incremental value of short-term serial change (over the immediate 48-hour treatment window) is limited. The cervix may exhibit reversible mechanical changes related to uterine activity, probe pressure, hydration, or measurement conditions. Such short-horizon variability may reflect “noise” more than stable biological progression, especially when the outcome is delivery weeks later. The wide observed range (−13 to +26 mm) supports that day-to-day measurement variation and transient physiology can be substantial.

Implications for teaching and practice

For trainees, this paper is a useful corrective against “more measurements = better prediction.” It supports a streamlined approach: in PTL, admission CL is valuable, but routine repeat CL after successful short-term tocolysis should not be expected to refine risk meaningfully and may consume resources without improving decision-making. In teaching, it pairs well with foundational asymptomatic screening studies: cervical length is powerful, but its optimal use depends on clinical context and what decision the measurement is meant to change (e.g., steroids/transfer vs reassurance/discharge).

Fonseca EB, Celik E, Parra M, Singh M, Nicolaides KH.
Progesterone and the risk of preterm birth among women with a short cervix. New England Journal of Medicine. 2007;357:462–469.

However, this strategy addressed only a small proportion of all spontaneous early preterm births, because the majority occur in women without a prior history. In parallel, transvaginal ultrasound (TVUS) screening studies had firmly established that asymptomatic mid-trimester cervical shortening is a powerful predictor of early spontaneous preterm delivery. What remained uncertain was whether progesterone could reduce preterm birth risk in women identified solely on the basis of a short cervix, irrespective of obstetric history. Fonseca and colleagues designed this landmark randomized controlled trial to test whether vaginal progesterone administered to women with a very short cervix detected at routine screening could prevent early preterm birth.

Objectives

  1. To determine whether vaginal progesterone reduces the rate of spontaneous delivery before 34 weeksin asymptomatic women with a short cervix identified at mid-gestation.
  2. To evaluate neonatal morbidity and safety associated with vaginal progesterone in this population.

 Methods

Study design: Multicenter, randomized, double-blind, placebo-controlled trial.

Screening population: Cervical length was measured by TVUS at a median gestational age of 22 weeks (range 20–25 weeks) in 24,620 pregnant women undergoing routine prenatal care. This very large screening base was critical to identify the relatively small proportion of women with extreme cervical shortening.

Eligibility and randomization:

  • Cervical length ≤15 mm was identified in 413 women (1.7%).
  • Of these, 250 women (60.5%) consented and were randomized to receive either vaginal progesterone or placebo.
  • Both singleton and twin pregnancies were included, although the majority were singletons.
  • Exclusion criteria included major fetal anomalies, active labor, ruptured membranes, or a cervical cerclage.

Intervention:

  • Vaginal progesterone 200 mg nightly, administered from 24 to 34 weeks’ gestation, versus identical placebo.
  • Treatment was self-administered and continued until 34 weeks or delivery.

Outcome measures:

  • Primary outcome: spontaneous preterm delivery before 34 weeks’ gestation.
  • Secondary outcomes: neonatal morbidity (composite outcomes), adverse events, and treatment safety.

Statistical analysis:

  • Analyses were performed on an intention-to-treat basis.
  • Relative risks (RRs) and 95% confidence intervals (CIs) were calculated to compare outcomes between groups.

 Main results

Primary outcome:
Spontaneous delivery before 34 weeks occurred significantly less often in the progesterone group than in the placebo group:

  • 19.2% in the progesterone group vs 34.4% in the placebo group
  • Relative risk: 0.56 (95% CI, 0.36–0.86)

This represents an approximate 44% reduction in early spontaneous preterm birth among women with a cervix ≤15 mm who received vaginal progesterone.

Neonatal outcomes:
Neonatal morbidity was lower in the progesterone group (8.1%) compared with placebo (13.8%), corresponding to a relative risk of 0.59, although this difference did not reach statistical significance (95% CI, 0.26–1.25; P = 0.17). Importantly, the direction of effect consistently favored progesterone.

Safety:
No serious adverse maternal or fetal events were associated with progesterone use. Compliance was high, and vaginal administration was well tolerated, reinforcing feasibility for population-based screening strategies.

Interpretation

This trial provided the first high-quality evidence that progesterone can prevent early spontaneous preterm birth in women without prior preterm birth, selected purely on the basis of sonographic cervical shortening. The magnitude of effect was clinically substantial, particularly given the extremely high baseline risk associated with a cervical length ≤15 mm.

The findings supported a paradigm shift: prevention of preterm birth could move beyond historical risk factors and toward ultrasound-based identification of current pregnancy risk. Importantly, the study demonstrated that cervical length screening is actionable—knowledge of risk can be paired with an effective, safe intervention.

Implications for teaching and clinical practice

For teaching purposes, this paper is pivotal because it:

  1. Establishes short cervix as a treatable condition, not merely a prognostic marker.
  2. Provides a strong evidence base for vaginal progesteroneas first-line therapy in asymptomatic women with a very short cervix.
  3. Lays the groundwork for later studies extending progesterone use to broader cervical length thresholds and supporting universal cervical length screening

This trial fundamentally reshaped modern preventive obstetrics by linking screening, pathophysiology, and intervention into a coherent, evidence-based framework.

Hassan SS, Romero R, Vidyadhari D, Fusey S, Baxter JK, Khandelwal M, et al.
Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter randomized double-blind placebo-controlled trial. Ultrasound in Obstetrics & Gynecology. 2011;38(1):18–31.

However, several critical questions remained unanswered:

  1. Would progesterone be effective across a broader range of cervical shortening, particularly the clinically pragmatic range of 10–20 mm?
  2. Could these findings be replicated in a large, rigorously designed, international multicenter trial?
  3. Would progesterone reduce not only preterm birth rates but also clinically meaningful neonatal morbidity?

The PREGNANT trial, led by Hassan and Romero, was designed to address these gaps. It represents one of the most methodologically robust intervention trials linking sonographic cervical length screening to preventive therapy, and it played a decisive role in shifting clinical guidelines toward progesterone-based prevention strategies.

Objectives

The primary objective was to determine whether micronized vaginal progesterone gel reduces the incidence of preterm birth before 33 weeks of gestation in asymptomatic women with a sonographically short cervix identified in the mid-trimester.

Secondary objectives included evaluating the effect of progesterone on:

  • Preterm birth at other gestational thresholds
  • Neonatal morbidity and mortality
  • Safety and tolerability of prolonged vaginal progesterone use

 Methods

Study design

This was a multicenter, randomized, double-blind, placebo-controlled trial, conducted under rigorous Good Clinical Practice standards.

Population and eligibility

Eligible participants were asymptomatic women with:

  • Singleton pregnancy
  • Gestational age between 19+0 and 23+6 weeks
  • Transvaginal ultrasound cervical length between 10 and 20 mm

Women were excluded if they had:

  • Symptoms of preterm labor
  • Ruptured membranes
  • Major fetal anomalies
  • Prior or current cervical cerclage

Importantly, women with and without a history of spontaneous preterm birth were included, allowing assessment of progesterone efficacy independent of obstetric history.

Randomization and intervention

A total of 465 women were randomized; after minimal loss to follow-up, 458 women were included in the intention-to-treat analysis. Participants were allocated to:

  • Vaginal progesterone gel (90 mg daily), or
  • Placebo gel, identical in appearance and administration

Treatment commenced between 20 and 23+6 weeks and continued until 36+6 weeks, rupture of membranes, or delivery—whichever occurred first. Randomization was stratified by center and history of prior preterm birth, strengthening internal validity.

Outcomes

  • Primary outcome: spontaneous preterm birth before 33 weeks
  • Secondary outcomes: preterm birth before other gestational ages, composite neonatal morbidity, and individual neonatal complications (e.g. respiratory distress syndrome, intraventricular hemorrhage)

Statistical analysis

The primary analysis was conducted on an intention-to-treat basis. Relative risks (RRs) with 95% confidence intervals were calculated. Multivariable models adjusted for potential confounders, including obstetric history and demographic factors.

Main results

Primary outcome

The rate of spontaneous preterm birth before 33 weeks was significantly lower in the progesterone group:

  • 8.9% (21/235) with progesterone
  • 16.1% (36/223) with placebo

This corresponded to a relative risk of 0.55 (95% CI, 0.33–0.92; P = 0.02), representing a 45% reduction in early preterm birth.

Secondary obstetric outcomes

Progesterone use was associated with consistent reductions in preterm birth across multiple gestational thresholds, reinforcing the robustness of the treatment effect. Importantly, the benefit was observed regardless of prior preterm birth history, demonstrating that cervical length–based risk stratification alone is sufficient to identify women who benefit from therapy.

Neonatal outcomes

Neonatal morbidity was significantly reduced in the progesterone group. Infants born to treated mothers had lower rates of:

  • Respiratory distress syndrome
  • Composite neonatal morbidity and mortality

These findings elevated the clinical relevance of the trial, demonstrating that progesterone not only prolongs gestation but also improves meaningful neonatal outcomes.

Safety

Vaginal progesterone was well tolerated, with no increase in maternal adverse events, congenital anomalies, or serious neonatal complications. Compliance was high, supporting feasibility in real-world clinical practice.

Interpretation

The PREGNANT trial provided definitive evidence that vaginal progesterone is an effective, safe intervention for asymptomatic women with a short cervix (10–20 mm). It extended prior findings in three crucial ways:

  1. Broader applicability:The benefit was shown across a wider cervical length range than earlier trials, aligning with common clinical thresholds used in screening programs.
  2. Independence from obstetric history:Efficacy did not depend on prior preterm birth, supporting a paradigm shift away from history-based prevention alone.
  3. Neonatal benefit:Demonstration of reduced neonatal morbidity strengthened the argument for population-level screening and intervention.

The trial also reinforced the concept that spontaneous preterm birth is frequently driven by premature cervical remodeling, which is amenable to hormonal modulation.

Implications for teaching and clinical practice

For medical students, residents, and fellows, this study is a cornerstone trial demonstrating how screening, pathophysiology, and therapy converge. It underpins current recommendations for vaginal progesterone as first-line therapy in women with a short cervix and strongly supports universal mid-trimester cervical length screening in singleton pregnancies.

Combs CA. Vaginal progesterone for asymptomatic cervical shortening and the case for universal screening of cervical length. American Journal of Obstetrics and Gynecology. 2012;206:124–130. (Editorial)

At the time of publication, the field was at an inflection point: high-quality trials had demonstrated that vaginal progesterone reduces preterm birth in women with a short cervix, yet universal screening had not been widely adopted, partly due to lingering skepticism about cost-effectiveness, generalizability, and clinical implementation.

The editorial addresses two interrelated but conceptually distinct clinical questions:

  1. If a short cervix is detected, is there an effective treatment that reduces preterm birth?
  2. If effective treatment exists, is it worthwhile to screen asymptomatic women to detect a short cervix?

Combs’ central thesis is that, by 2011–2012, the accumulated evidence had answered both questions affirmatively, thereby justifying a shift toward universal mid-trimester cervical length screening in singleton pregnancies.

Context: short cervix as a high-risk condition

The editorial begins by reaffirming a key principle derived from earlier cohort studies: a short cervix detected by transvaginal sonography in midpregnancy confers a high risk of early spontaneous preterm birth. Importantly, risk increases as cervical length shortens and as shortening is detected earlier in gestation. This association is robust, reproducible, and biologically plausible, reflecting premature cervical remodeling.

However, Combs emphasizes that risk identification alone is insufficient. Screening can be harmful if it merely labels women as “high risk” without offering effective interventions, potentially increasing anxiety and encouraging the use of unproven or harmful therapies. Historically, such therapies included bed rest, activity restriction, long-term tocolysis, and empiric antibiotics—interventions lacking evidence and, in some cases, associated with harm.

Evaluation of available treatments for short cervix

Cervical cerclage

The editorial provides a nuanced appraisal of cerclage. By the early 2000s, cerclage had shown benefit in a narrowly defined subgroup: women with singleton pregnancies, a history of spontaneous preterm birth, and a short cervix detected in the mid-trimester. In this group, cerclage reduced preterm birth and neonatal morbidity.

In contrast, cerclage did not reduce preterm birth in women without prior preterm birth and was shown to be ineffective or harmful in twin pregnancies. As a result, cerclage could not serve as a universal response to cervical shortening detected through population-wide screening.

Vaginal progesterone

Combs then focuses on vaginal progesterone, which he presents as a transformative intervention. Drawing on randomized controlled trials and, critically, an individual patient data meta-analysis (Romero et al.), the editorial highlights several decisive findings:

  • Vaginal progesterone reduces early preterm birth (<33 weeks) in asymptomatic women with a short cervix.
  • The effect size is substantial, with reductions in early preterm birth of approximately 40–45%.
  • Benefits extend to neonatal morbidity, not merely gestational prolongation.
  • Crucially, the benefit is observed regardless of prior preterm birth history.

This last point is central to the editorial’s argument. Unlike cerclage, progesterone does not require prior obstetric history to identify beneficiaries; cervical length alone is sufficient.

Evidence synthesis and interpretation

A major strength of the editorial is its emphasis on individual patient data meta-analysis, which allows harmonized reanalysis across trials. Combs underscores that this approach revealed insights not apparent in individual studies:

  • The benefit of progesterone was consistent across different cervical length subgroups (e.g., 10–20 mm, ≤15 mm), although statistical significance was strongest where sample size was greatest.
  • Efficacy was similar whether progesterone was administered as 90 mg vaginal gel or 200 mg micronized capsules, suggesting a class effect rather than formulation-specific benefit.
  • Treatment effects were stable across subgroups defined by obstetric history, reinforcing generalizability.

By emphasizing these points, Combs addresses a common critique of earlier trials—that results might be driven by narrow inclusion criteria or specific formulations.

The case for universal cervical length screening

Having established that vaginal progesterone is effective, safe, and broadly applicable, the editorial turns to the second major question: Should asymptomatic women be screened to detect a short cervix?

Combs argues that screening is justified when three conditions are met:

  1. The condition is common enough and clinically important.
  2. The screening test is accurate, acceptable, and reproducible.
  3. An effective intervention exists that improves meaningful outcomes.

He argues that cervical length screening satisfies all three. Transvaginal ultrasound is safe, well tolerated, and already widely used. Short cervix is a strong predictor of early preterm birth, which carries disproportionate morbidity and mortality. Vaginal progesterone provides a low-risk, effective intervention.

The editorial also addresses cost-effectiveness indirectly, noting that preventing early preterm births yields disproportionate benefits in terms of neonatal outcomes and healthcare costs, even if only a small fraction of screened women receive treatment.

Educational and clinical implications

For teaching purposes, this editorial is particularly valuable because it demonstrates how evidence transitions into policy and practice. It synthesizes epidemiology, randomized trials, and meta-analytic data to justify a population-level preventive strategy. It also illustrates how different interventions (cerclage vs progesterone) have distinct evidence-based indications, underscoring the importance of personalized, mechanism-based care.

Conclusion

Combs’ editorial represents a pivotal moment in the evolution of preterm birth prevention. It articulates a coherent, evidence-based argument that doing nothing is no longer acceptable: effective therapy exists, and failure to screen denies women and infants a proven benefit. The article helped solidify professional momentum toward universal mid-trimester cervical length screening with targeted vaginal progesterone therapy, a strategy now embedded in many contemporary clinical guidelines.

Campbell S. Universal cervical-length screening and vaginal progesterone prevents early preterm births, reduces neonatal morbidity and is cost saving: doing nothing is no longer an option. Ultrasound in Obstetrics & Gynecology. 2011;38:1–9. (Editorial)

Unlike primary research articles, its purpose is to frame the accumulated evidence within a public health and policy perspective, explicitly asking whether modern obstetrics can justify not implementing universal cervical length screening given the burden of preterm birth and the availability of effective intervention.

Campbell writes at a moment when preterm birth rates had remained stubbornly high for decades despite advances in neonatal care. The editorial’s core argument is normative and strategic: once an effective, safe, and cost-saving preventive strategy exists, inaction becomes ethically and clinically indefensible.

The scale and impact of the problem

The editorial begins by emphasizing the magnitude of preterm birth as a global health problem. Preterm birth is presented not merely as a clinical complication but as the leading cause of neonatal mortality and a dominant driver of long-term childhood morbidity in developed countries. Campbell stresses that although births before 37 weeks define prematurity, the greatest burden of death, disability, and cost arises from early preterm birth (<32–33 weeks).

He details both short-term neonatal complications (respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, sepsis) and long-term outcomes (cerebral palsy, cognitive impairment, behavioral disorders). Importantly, the editorial expands beyond medical outcomes to highlight psychosocial and economic consequences for families and society, including marital stress, lifelong disability care, and enormous healthcare expenditure.

This framing establishes why even modest reductions in early preterm birth can yield disproportionately large benefits.

Limitations of historical approaches

Campbell places current evidence in historical context. For decades, obstetrics relied on interventions such as bed rest, hydration, tocolysis, and antibiotics—approaches aimed largely at treating symptoms rather than underlying mechanisms. These strategies failed to reduce population-level prematurity rates.

Progesterone’s history is described as illustrative: early trials failed because they were based on incorrect assumptions about progesterone withdrawal in human pregnancy. Subsequent, better-designed studies using appropriate formulations and routes of administration demonstrated benefit, but only once pathophysiology and patient selection were correctly aligned.

This historical reflection reinforces a central theme: preterm birth prevention succeeds only when intervention targets the correct biological pathway in the correct population.

Cervical length screening as a risk stratification tool

Campbell reiterates that transvaginal ultrasound measurement of cervical length in the mid-trimester is one of the strongest predictors of spontaneous early preterm birth. He emphasizes that cervical shortening is detectable weeks before clinical symptoms, allowing for true prevention rather than crisis management.

The editorial highlights that cervical length screening satisfies classic criteria for a successful screening test:

  • The condition is common and serious
  • The test is safe, acceptable, and reproducible
  • High-risk individuals can be identified before irreversible harm occurs

Unlike many obstetric screening tests, cervical length directly identifies a modifiable risk state.

Vaginal progesterone as an effective intervention

Campbell synthesizes evidence from randomized trials demonstrating that daily vaginal progesterone administered to women with a short cervix significantly reduces early preterm birth and neonatal morbidity. He underscores that progesterone is:

  • Biologically plausible
  • Clinically effective
  • Well tolerated
  • Free of known serious maternal or fetal adverse effects

Crucially, progesterone’s benefit is shown in asymptomatic women, meaning that screening identifies candidates before preterm labor begins—an essential feature of effective prevention.

Cost-effectiveness and health economics

A distinctive contribution of this editorial is its emphasis on economic modeling. Campbell discusses analyses demonstrating that universal cervical length screening followed by progesterone treatment in women with a short cervix is cost saving, not merely cost effective.

The argument rests on several points:

  • Only a small proportion of screened women require treatment
  • Progesterone is inexpensive
  • Preventing even a small number of very early preterm births offsets screening costs due to massive neonatal intensive care savings

Campbell argues that focusing narrowly on the cost of screening misses the broader economic reality: early preterm birth is extraordinarily expensive, and preventing it yields long-term savings extending well beyond the neonatal period.

Ethical and policy implications

The editorial’s most forceful section is its ethical argument. Campbell asserts that when evidence demonstrates that a strategy prevents death, disability, and suffering at acceptable or reduced cost, failure to implement that strategy constitutes a failure of care.

He explicitly challenges inertia in clinical practice and guideline development, noting that obstetrics has historically been slow to adopt preventive strategies even when evidence is compelling. The title’s concluding phrase—“doing nothing is no longer an option”—is not rhetorical but prescriptive.

Limitations and scope

Campbell acknowledges that the evidence base applies primarily to singleton pregnancies and that screening programs require proper training, standardization, and quality assurance. He does not advocate indiscriminate intervention but rather structured, evidence-based implementation.

The editorial also recognizes that progesterone reduces—but does not eliminate—preterm birth risk, reinforcing the need for ongoing research into complementary strategies.

Educational and clinical significance

For learners and clinicians, this editorial is important because it illustrates how clinical trial evidence translates into public health policy. It demonstrates the shift from reactive obstetrics to preventive care and highlights the importance of aligning screening, intervention, and outcomes of highest clinical relevance (early preterm birth).

It also serves as a model for how clinicians should evaluate new screening programs: not only by statistical significance, but by clinical impact, cost, and ethical responsibility.

Conclusion

Campbell’s editorial represents a decisive call to action. It synthesizes epidemiology, randomized trial evidence, neonatal outcomes, and health economics to argue that universal mid-trimester cervical length screening with targeted vaginal progesterone therapy should become standard care in singleton pregnancies. In doing so, it frames prevention of early preterm birth as both a scientific and moral imperative in modern obstetrics.

Berghella V, Odibo AO, Tolosa JE. Cerclage for prevention of preterm birth in women with a short cervix found on transvaginal ultrasound examination: a randomized trial. American Journal of Obstetrics and Gynecology. 2004;191:1311–1317.

As TVUS emerged as a more accurate tool for identifying cervical shortening, an important clinical question arose: should cerclage be placed solely on the basis of a short cervix detected by ultrasound, regardless of prior obstetric history?

Early observational data suggested that a short cervix was strongly associated with spontaneous preterm birth (sPTB), but whether intervening surgically in this situation would improve outcomes was uncertain. At the time, cerclage was already controversial due to inconsistent trial results, potential procedure-related morbidity, and lack of clarity regarding patient selection. Berghella and colleagues designed this randomized trial to directly test whether cerclage prevents preterm birth in women with a short cervix detected on TVUS, compared with conservative management.

Objectives

The primary objective was to determine whether cervical cerclage, compared with bed rest alone, reduces the rate of preterm birth before 35 weeks’ gestation in women with a sonographically short cervix. Secondary objectives included evaluation of other obstetric and neonatal outcomes and subgroup analyses based on risk profile.

Methods

Study design

This was a prospective, randomized controlled trial, conducted at two tertiary academic centers in the United States.

Population and screening strategy

Women were eligible if they had one or more recognized risk factors for preterm birth, including:

  • Prior preterm birth before 35 weeks
  • Two or more prior cervical dilatation and curettage procedures
  • Diethylstilbestrol exposure
  • Prior cervical surgery (e.g. cone biopsy)
  • Müllerian anomalies
  • Twin pregnancy

These women underwent serial transvaginal ultrasound cervical length screening every two weeks from 14 weeks to 23 weeks + 6 days of gestation. In addition, a small number of low-risk women with incidentally detected cervical shortening were also included.

Inclusion criteria for randomization

Women were offered randomization if TVUS identified:

  • A cervical length <25 mm, and/or
  • Significant cervical funneling (>25%)

Importantly, women were asymptomatic at the time of detection; those with active contractions, ruptured membranes, or other contraindications were excluded.

Randomization and intervention

A total of 61 women consented and were randomized:

  • 31 to receive McDonald cervical cerclage, plus bed rest
  • 30 to receive bed rest alone

Both groups received similar counseling and obstetric management apart from the surgical intervention.

Outcomes

  • Primary outcome: preterm birth before 35 weeks’ gestation
  • Secondary outcomes: gestational age at delivery, neonatal outcomes, and obstetric complications

Statistical analysis focused on relative risk estimates with 95% confidence intervals. Subgroup analyses were performed, particularly in women with singleton pregnancies and prior preterm birth.

Main results

Baseline characteristics

The two groups were well balanced with respect to maternal age, parity, obstetric history, cervical length at enrollment, and gestational age at randomization. Approximately 77% of pregnancies were high-risk singleton gestations, with the remainder including twins and lower-risk cases.

Primary outcome

Preterm birth before 35 weeks occurred in:

  • 45% (14/31) of women in the cerclage group
  • 47% (14/30) of women in the bed rest group

This corresponded to a relative risk of 0.94 (95% CI, 0.34–2.58), indicating no statistically or clinically significant reduction in preterm birth with cerclage.

Secondary outcomes

There were no significant differences between groups in:

  • Gestational age at delivery
  • Rates of very preterm birth
  • Neonatal outcomes

Procedure-related complications were not emphasized as a major issue, but the absence of benefit meant that even low complication rates could not justify routine use.

Subgroup analysis

In a subgroup of 31 singleton pregnancies with a prior preterm birth <35 weeks and a short cervix (<25 mm), recurrent preterm birth occurred in:

  • 40% of the cerclage group
  • 56% of the bed rest group

Although numerically lower in the cerclage group, this difference was not statistically significant (RR 0.52; 95% CI, 0.12–2.17). The wide confidence intervals reflect the small sample size and limited power of the study to detect moderate treatment effects.

Interpretation

The central finding of this trial is negative: cerclage did not prevent preterm birth in women with a short cervix detected on transvaginal ultrasound when applied broadly to a mixed-risk population. This result challenged the intuitive assumption that mechanically reinforcing a shortened cervix would improve outcomes and highlighted the importance of appropriate patient selection.

The authors emphasize that cervical shortening is not a uniform pathological entity. In many women, it may represent an early manifestation of inflammatory, infectious, or biochemical pathways that are not corrected by mechanical support alone. This insight foreshadowed later work demonstrating that cerclage benefits only specific subgroups, rather than all women with cervical shortening.

Implications for clinical practice and teaching

This study is critical for understanding why cerclage should not be used indiscriminately in women with a short cervix. For trainees, it illustrates a key principle of evidence-based obstetrics: strong risk prediction does not automatically imply that a given intervention will be effective.

In combination with later trials and meta-analyses, this study contributed to the modern consensus that cerclage is beneficial only in a narrowly defined subgroup—primarily women with singleton pregnancies, a prior spontaneous preterm birth, and a short cervix—while vaginal progesterone offers a broader, less invasive, and more generalizable preventive strategy.

Vayssière C, Favre R, Audibert F, Chauvet MP, Gaucherand P, Tardif D, et al.; GROG Study Group.
Cervical assessment at 22 and 27 weeks for the prediction of spontaneous birth before 34 weeks in twin pregnancies: is transvaginal sonography more accurate than digital examination? Ultrasound in Obstetrics & Gynecology. 2005;26:707–712.

In this context, clinicians have historically relied on digital cervical examination, including the Bishop score and related composite indices, to estimate preterm birth risk. However, evidence from singleton pregnancies had already shown that digital examination is subjective and inferior to transvaginal ultrasound (TVUS) cervical length measurement.

Whether these conclusions could be extrapolated to twin pregnancies was uncertain. Cervical shortening is common in twins, but its predictive accuracy, optimal timing, and relative performance compared with digital examination remained debated. Vayssière and colleagues designed this prospective multicenter study to directly compare digital and sonographic cervical assessment in twin pregnancies, focusing on clinically relevant early preterm birth (<34 weeks).

Objectives

The study aimed to:

  1. Compare the accuracy of transvaginal sonographic cervical assessment(cervical length and cervical index) with digital examination (Bishop score and cervical score) for predicting spontaneous birth before 34 weeks in twin pregnancies.
  2. Evaluate whether predictive performance differs when assessment is performed at 22 weeks versus 27 weeksof gestation.

 

Methods

Study design

This was a prospective multicenter observational study, conducted within the French GROG (Research Group in Obstetrics and Gynecology) network.

Study population

The study included twin pregnancies attending for routine ultrasound examination at two gestational windows:

  • 22-week group: 175 women
  • 27-week group: 153 women

All women had viable twin pregnancies and were undergoing scheduled assessment. The study population reflects routine clinical practice rather than a highly selected high-risk subgroup.

Cervical assessment protocol

Each participant underwent two consecutive cervical assessments during the same visit:

  1. Digital examination (performed first):
    • Bishop score (composite score including dilation, effacement, consistency, position, and station)
    • Cervical score (defined as cervical length minus cervical dilatation, both estimated manually)
  2. Transvaginal ultrasound examination:
    • Cervical length measured in millimeters
    • Funnel length assessed
    • Cervical index calculated as:
      1 + (funnel length / cervical length)

The sequential order (digital first, ultrasound second) minimized bias from sonographic knowledge influencing digital assessment.

Outcomes

The primary outcome was spontaneous delivery before 34 weeks of gestation, chosen because it represents a threshold associated with substantial neonatal morbidity in twin pregnancies.

Statistical analysis

  • Associations between cervical parameters and outcome were assessed using non-parametric tests (Mann–Whitney U-test).
  • Receiver–operating characteristic (ROC) curves were constructed for each parameter at each gestational age.
  • Areas under the ROC curve (AUCs) were compared to determine relative predictive accuracy.
  • Optimal cut-off values were used to calculate likelihood ratios for clinical interpretation.

 

Main results

Overall outcomes

In the 22-week group, spontaneous delivery before 34 weeks occurred in 10.9% of women (19/175).
In the 27-week group, the corresponding rate was 9.2% (14/153).

Median gestational age at delivery in both groups was approximately 36 weeks, illustrating that many twin pregnancies reach late preterm or term gestation despite elevated baseline risk.

Findings at 22 weeks

At 22 weeks, all four cervical parameters—cervical length, cervical index, Bishop score, and cervical score—were statistically associated with delivery before 34 weeks. However:

  • The areas under the ROC curves for ultrasound-based and digital parameters did not differ significantly.
  • This suggests that, at 22 weeks in twins, digital examination and transvaginal sonography perform similarly in predicting early preterm birth.

Median cervical length at 22 weeks was 40 mm, with a wide range (6–65 mm), highlighting substantial interindividual variability in twins.

 

Findings at 27 weeks

At 27 weeks, results diverged more clearly between methods:

  • All ultrasound-based parameters (cervical length and cervical index) remained significant predictors of delivery before 34 weeks.
  • Digital examination performed worse: the Bishop score was no longer a significant predictor.

Median cervical length at 27 weeks was 35 mm (range 1–57 mm), reflecting physiological shortening with advancing gestation.

Critically, transvaginal sonography outperformed digital examination at this later gestational age.

Diagnostic performance

Using a clinically relevant cutoff of cervical length ≤25 mm at 27 weeks:

  • Positive likelihood ratio: 5.4 (range 3.2–9.0)
  • Negative likelihood ratio: 0.3 (range 0.1–0.7)

By comparison, the cervical score ≤1 (digital measure) yielded weaker likelihood ratios (positive ~2.3; negative ~0.6).

The cervical index demonstrated the largest AUC overall and was significantly superior to both the Bishop score and cervical score at 27 weeks.

Interpretation

This study provides several important insights specific to twin pregnancies:

  1. Predictive accuracy depends on gestational age.
    At 22 weeks, digital and ultrasound assessments perform similarly, possibly because cervical remodeling in twins may still be subtle and diffuse at this stage.
  2. Transvaginal ultrasound becomes superior later in pregnancy.
    By 27 weeks, ultrasound-based measures—particularly cervical length and cervical index—clearly outperform digital examination, likely because ultrasound captures objective structural changes that digital examination cannot reliably detect.
  3. Cervical shortening remains clinically meaningful in twins.
    Despite differences in pathophysiology between singleton and twin pregnancies, cervical length retains prognostic value for early preterm birth.

  4. Implications for clinical practice and teaching

    This study is highly instructive for trainees because it highlights that evidence from singleton pregnancies cannot be uncritically extrapolated to twins. While transvaginal ultrasound is clearly superior later in gestation, the overall predictive performance in twins is lower than in singletons, and—crucially—effective preventive interventions (progesterone, cerclage) do not have the same benefit profile.

    The paper reinforces why, despite strong predictive associations, routine intervention based on cervical shortening in twin pregnancies remains controversial, and why screening must be carefully aligned with available evidence-based treatments.

Muller M, Aït-Belkacem D, Hessabi M, Gennisson JL, Grangé G, Goffinet F, Lecarpentier E, Cabrol D, Tanter M, Tsatsaris V.
Assessment of the cervix in pregnant women using shear wave elastography: a feasibility study. Ultrasound in Medicine & Biology. 2015;41(11):2789–2797.

These biomechanical changes may precede measurable shortening and could theoretically offer earlier or complementary risk information.

Historically, attempts to quantify cervical stiffness included invasive devices such as cervicotonometers, which demonstrated prognostic value but were unsuitable for routine practice due to invasiveness and poor acceptability. Advances in ultrasound physics have enabled elastography, a non-invasive technique that estimates tissue stiffness. Among these, shear wave elastography (SWE) allows quantitative measurement of tissue stiffness based on shear wave propagation speed, potentially overcoming the subjectivity and operator dependence of earlier static elastography methods.

Muller and colleagues conducted this feasibility study to explore whether SWE could be applied to the pregnant cervix in vivo and whether measurable differences in cervical stiffness are associated with preterm labor or preterm delivery.

Objectives

The primary objectives of the study were:

  1. To assess the technical feasibilityof shear wave elastography for in vivo evaluation of the pregnant cervix.
  2. To quantify cervical stiffness, expressed as shear wave speed (SWS), in pregnant women.
  3. To explore whether cervical stiffness differs between women with preterm labor, those who subsequently deliver preterm, and those who deliver at term.

Importantly, the study was exploratory and not designed to establish clinical cutoffs or predictive algorithms.

Methods

Study design

This was a cross-sectional feasibility study, conducted at a tertiary maternity center.

Study population

A total of 157 pregnant women were included. The population comprised:

  • Women with uncomplicated pregnancies
  • Women diagnosed with preterm labor
  • Women who ultimately delivered preterm

Gestational ages varied, reflecting real-world clinical diversity rather than a narrowly selected screening population.

Shear wave elastography technique

Shear wave elastography was performed using supersonic shear imaging, an advanced ultrasound technique that generates shear waves within tissue and measures their propagation speed. Because shear waves travel faster in stiffer tissue, shear wave speed (SWS) serves as a quantitative surrogate for tissue stiffness.

Key technical aspects included:

  • Measurement focused on the lower anterior portion of the cervix, selected for accessibility, reproducibility, and reduced motion artifacts.
  • A standardized 8-mm region of interest (ROI) was used to ensure consistency.
  • Care was taken to minimize probe pressure, as excessive compression could artificially alter stiffness measurements.
  • Multiple measurements were obtained to assess reproducibility.

Unlike static elastography, SWE does not rely on manual compression, enhancing objectivity.

Outcomes and comparisons

The primary outcome was cervical SWS, expressed quantitatively. Comparisons were made between:

  • Women with vs without a diagnosis of preterm labor
  • Women who delivered preterm vs those who delivered at term

No intervention was performed, and clinical management was not altered by elastography findings.

Main results

Feasibility and technical performance

Shear wave elastography was technically feasible in the vast majority of participants. Adequate measurements could be obtained without causing discomfort or adverse effects. This was a critical finding, as the pregnant cervix presents unique challenges related to depth, mobility, and anatomical variability.

The study demonstrated that quantitative stiffness measurements of the cervix are possible in vivo, representing a methodological advance over prior qualitative or semi-quantitative approaches.

Cervical stiffness findings

The key physiological observation was that cervical shear wave speed was slightly but significantly lower in:

  • Women diagnosed with preterm labor, and
  • Women who subsequently delivered preterm,

compared with women who delivered at term.

Lower shear wave speed indicates softer cervical tissue, consistent with premature cervical remodeling. Although differences were modest in absolute terms, they were statistically significant, suggesting that SWE captures biologically meaningful variation.

Relationship to cervical length

The study reinforces the concept that cervical remodeling is multidimensional. While cervical length reflects macroscopic geometry, shear wave elastography reflects tissue mechanical properties. Importantly, stiffness changes may occur before or independently of shortening, raising the possibility that elastography could detect early pathological changes not visible on conventional ultrasound.

However, the study did not establish direct predictive superiority over cervical length, nor was it powered to do so.

Interpretation

This feasibility study provides proof-of-concept that quantitative biomechanical assessment of the cervix is achievable during pregnancy using shear wave elastography. The finding that women with preterm labor or preterm delivery have measurably softer cervixes supports long-standing physiological models in which cervical softening is a critical early event in the pathway to preterm birth.

Crucially, the authors emphasize that SWE should be viewed as complementary rather than competitive with cervical length measurement. While cervical length remains the most validated predictor, elastography could enrich risk stratification by capturing aspects of cervical remodeling that length alone cannot.

Implications for research, teaching, and future practice

For learners, this study is valuable because it illustrates the next frontier of cervical assessment. It reinforces that cervical length is not the full story and that biomechanics matter. The paper also serves as an example of how technological innovation enters clinical research: starting with feasibility, then moving toward validation, standardization, and outcome-driven trials.

From a research perspective, the study opens several avenues:

  • Longitudinal studies to assess whether stiffness changes precede shortening
  • Integration of elastography with cervical length in multivariable risk models
  • Evaluation of whether progesterone or other interventions modify cervical stiffness trajectories

At present, shear wave elastography remains investigational and should not be used for routine clinical decision-making. Nevertheless, it represents a promising adjunct that may, in the future, refine prediction of spontaneous preterm birth.

Conclusion

Muller et al. demonstrate that shear wave elastography is a feasible, non-invasive method for assessing cervical stiffness during pregnancy and that reduced stiffness is associated with preterm labor and preterm delivery. While not ready for clinical implementation, this study advances understanding of cervical remodeling and highlights the potential of biomechanical assessment to complement traditional cervical length measurement.

Reicher L, Fouks Y, Yogev Y. Cervical assessment for predicting preterm birth—cervical length and beyond. Journal of Clinical Medicine. 2021;10:627. 

However, accumulating evidence suggested that cervical length alone captures only one dimension of a complex, multifactorial biological process. Reicher, Fouks, and Yogev authored this comprehensive narrative review to synthesize contemporary knowledge on cervical assessment for preterm birth prediction, situating cervical length within a broader framework that includes cervical biology, timing of assessment, population-specific considerations, and emerging diagnostic technologies.

The review is explicitly translational in intent: it aims not only to summarize evidence but also to clarify how, when, and in whom cervical assessment should be used, while critically evaluating whether newer approaches can meaningfully improve prediction beyond cervical length.

Conceptual framework: preterm parturition syndrome

The authors ground their discussion in the concept of the preterm parturition syndrome, originally articulated by Romero and colleagues. In this model, spontaneous preterm birth is not a single disease but a final common pathway resulting from heterogeneous processes, including infection, inflammation, uteroplacental ischemia, stress, endocrine dysregulation, and mechanical factors.

Within this framework, cervical remodeling—shortening, softening, and dilation—is viewed as a downstream manifestation of upstream pathology. Cervical shortening may therefore be an early marker rather than the primary cause of preterm birth. This conceptualization is critical because it explains both the strength and limitations of cervical length as a predictor: it is robust, but not universally predictive, and not all short cervixes represent the same biological process.

Cervical length as a predictor of spontaneous preterm birth

Evidence base

The review synthesizes data from large prospective cohort studies and randomized trials demonstrating that mid-trimester cervical length is inversely related to sPTB risk, regardless of obstetric history. The authors emphasize that risk increases continuously as cervical length shortens, with particularly high risk below commonly used thresholds such as 25 mm.

Women with both a prior preterm birth and a short cervix represent the highest-risk group, but the review stresses that most spontaneous early preterm births occur in women without prior history, underscoring the importance of current-pregnancy assessment.

Optimal timing of measurement

Reicher et al. review evidence supporting cervical length screening between 16 and 24 weeks of gestation, noting that:

  • Measurement before 16 weeks has poor predictive accuracy in asymptomatic women.
  • Routine screening after 24 weeks is generally not recommended in asymptomatic women, as most interventional trials initiated therapy by this gestational age.

Nevertheless, the authors acknowledge that detection of a short cervix later in gestation may still inform clinical decisions such as antenatal corticosteroid administration or transfer to higher-level care.

Preferred measurement technique

The review reinforces that TVUS is the gold standard for cervical length measurement. Transabdominal and transperineal approaches are discussed but clearly identified as inferior due to poorer sensitivity, greater operator dependence, and susceptibility to confounding factors such as bladder filling and fetal position.

Importantly, the authors highlight that all major intervention trials demonstrating benefit (progesterone, cerclage) relied on TVUS-based measurement, reinforcing its central role.

Population-specific considerations

Singleton pregnancies

In singleton pregnancies, cervical length screening has the strongest evidence base. The review summarizes randomized trials showing that vaginal progesterone reduces preterm birth in women with a short cervix, regardless of obstetric history, and that cerclage is beneficial in a narrower subgroup (prior sPTB plus short cervix).

Twin pregnancies

The authors carefully distinguish twin pregnancies, noting that while cervical shortening is predictive of sPTB, interventions effective in singletons do not translate reliably to twins. Evidence for progesterone or cerclage in twins with a short cervix is inconsistent or negative, limiting the clinical utility of screening unless effective interventions are identified.

Special populations

Women with prior cervical surgery, uterine anomalies, or other risk factors are discussed, with the authors emphasizing individualized assessment rather than blanket recommendations.

Beyond cervical length: emerging modalities

A central contribution of this review is its structured discussion of novel cervical assessment techniques aimed at improving prediction beyond cervical length.

Cervical elastography

Both static and dynamic elastography are reviewed. The authors explain that elastography assesses cervical stiffness, a biomechanical property closely linked to cervical remodeling. While early studies—including shear wave elastography—suggest that cervical softening is associated with preterm birth, the review highlights significant limitations: lack of standardization, inter-device variability, and absence of validated clinical cutoffs.

Biochemical and molecular markers

The review briefly discusses biomarkers such as fetal fibronectin and inflammatory markers, noting that while they may provide complementary information, none have supplanted cervical length in routine asymptomatic screening.

Multimodal approaches

Reicher et al. suggest that future prediction models may integrate cervical length, biomechanical assessment, biomarkers, and clinical risk factors into composite risk scores, but stress that such models require rigorous validation.

Strengths and limitations of the evidence

The authors are careful to distinguish predictive accuracy from clinical utility. While many approaches show statistical association with preterm birth, few have demonstrated that their use changes management in a way that improves outcomes.

They also note heterogeneity across studies in terms of populations, gestational age at assessment, outcome definitions, and intervention thresholds, complicating direct comparisons.

Educational and clinical implications

For learners and clinicians, this review serves as a conceptual synthesis rather than a practice guideline. It clarifies why cervical length remains central, why it should not be overinterpreted, and why new technologies must be judged not only by novelty but by incremental clinical value.

The review is particularly valuable pedagogically because it connects pathophysiology, imaging, clinical trials, and guideline development into a coherent narrative.

Conclusion

Reicher and colleagues conclude that cervical length measured by transvaginal ultrasound remains the most validated and clinically useful tool for predicting spontaneous preterm birth, particularly in singleton pregnancies. While emerging technologies such as elastography offer intriguing insights into cervical biology, they remain investigational.

The future of preterm birth prediction likely lies not in replacing cervical length, but in augmenting it with complementary assessments once these approaches are standardized, validated, and shown to improve outcomes. Until then, cervical length screening—embedded within evidence-based intervention pathways—remains the cornerstone of preventive obstetrics.

course outline (90 mn)

Time: 0–7 min

  • Clinical relevance of spontaneous preterm birth
    Brief epidemiology emphasizing early preterm birth as the main driver of neonatal morbidity, mortality, and costs.
  • Why the cervix matters
    Introduce cervical length as the strongest antenatal predictor currently available.
  • Learning objectives
    At the end of the session, learners should be able to interpret cervical length, choose evidence-based interventions, and avoid ineffective or harmful practices.

Time: 7–15 min

  • Definitions and phenotypes of preterm birth
    Distinguish spontaneous vs indicated preterm birth; emphasize early (<34 weeks) vs late preterm birth.
  • Population burden
    Highlight that a small proportion of pregnancies account for a large share of early preterm births.
  • Concept of risk concentration
    Introduce epidemiologic rationale for screening based on cervical length distribution.

Time: 15–23 min

  • Structural anatomy of the cervix
    Collagen-rich extracellular matrix, smooth muscle content, and biomechanical role.
  • Physiology of cervical competence
    Maintenance of pregnancy through structural integrity and hormonal environment.
  • Physiologic cervical remodeling at term
    Softening, shortening, and dilation as a controlled biological process.

Time: 23–33 min

  • Preterm parturition syndrome framework
    Multiple upstream mechanisms converging on cervical change.
  • Inflammatory and infectious pathways
    Cytokine-mediated collagen degradation and prostaglandin activation.
  • Mechanical and vascular factors
    Uterine overdistension, ischemia, and stress-related mechanisms.
  • Clinical implication
    Cervical shortening as a marker rather than a single disease entity.

Time: 33–45 min

  • Historical cohort evidence
    Landmark studies establishing inverse relationship between cervical length and sPTB.
  • Risk as a continuum
    Interpretation of percentiles and thresholds (e.g. 25 mm).
  • Interaction with obstetric history
    Prior preterm birth + short cervix as the highest-risk phenotype.
  • Limits of prediction
    Distinguish prediction from determinism.

Time: 45–55 min

  • Transvaginal ultrasound as gold standard
    Superiority over digital and transabdominal approaches.
  • Technical requirements
    Bladder status, probe pressure, landmark identification.
  • Measurement variability and quality control
    Importance of training and standardized protocols.

Time: 55–63 min

  • Optimal screening window (16–24 weeks)
    Alignment with predictive accuracy and interventional trials.
  • Targeted vs universal screening
    Rationale for population-based approaches in singleton pregnancies.
  • Consequences of late detection
    Reduced preventive opportunity after 24 weeks.

Time: 63–75 min

  • Biological rationale for progesterone therapy
    Anti-inflammatory effects and maintenance of uterine quiescence.
  • Key randomized trials and meta-analytic evidence
    Reduction of early preterm birth and neonatal morbidity.
  • Clinical indications and practical use
    Candidate selection, formulations, dosage, duration.
  • Counseling and expectations
    Risk reduction vs risk elimination.

Time: 75–83 min

  • Mechanism of action
    Mechanical support vs biological modulation.
  • Evidence from randomized trials
    Benefit restricted to prior sPTB + short cervix in singleton pregnancies.
  • What cerclage does NOT do
    Lack of benefit in low-risk women and twins.

Time: 83–88 min

  • Twin pregnancies
    Predictive value of cervical length but absence of effective interventions.
  • Threatened preterm labor
    Role and limits of cervical length after symptoms develop.
  • Prior cervical surgery or insufficiency
    Individualized interpretation and management.

Time: 88–90 min

  • Core principles recap
    Cervical length as cornerstone of prediction; progesterone as first-line therapy; selective cerclage.
  • Clinical paradigm shift
    From reactive obstetrics to preventive care.
Simulated Clinical Cases

Case description

A 29-year-old primigravida is referred at 21+4 weeks’ gestation after a routine second-trimester ultrasound. Her pregnancy has been uncomplicated. She has no history of cervical surgery, uterine anomalies, or preterm birth. She is asymptomatic, with no uterine contractions, vaginal bleeding, or pelvic pressure.

Transvaginal ultrasound performed for cervical assessment shows:

  • Cervical length: 18 mm
  • No cervical funneling
  • Closed external os

There is no evidence of infection, and fetal anatomy is normal. The patient is anxious after being told that her cervix is “short” and asks about the risk to her pregnancy and possible treatments.

Questions raised by the case

  1. How should the risk of spontaneous preterm birth be interpreted in this patient?
  2. What is the most evidence-based management strategy?
  3. Should cervical cerclage be proposed?

Detailed answer and reasoning

  1. Risk interpretation
    This patient has asymptomatic mid-trimester cervical shortening, detected at an optimal screening window (16–24 weeks). A cervical length of 18 mmplaces her well below the commonly used 25 mm threshold and within a range associated with a markedly increased risk of early spontaneous preterm birth, even in the absence of prior obstetric history.

Importantly, cervical length functions as a continuous risk marker. Although she has no prior preterm birth, evidence shows that most early spontaneous preterm births occur in women without such history. Therefore, her lack of prior risk factors does not negate the prognostic significance of the finding.

  1. Evidence-based management
    The most evidence-based intervention is vaginal progesterone therapy.

Randomized controlled trials have consistently demonstrated that vaginal progesterone significantly reduces the risk of spontaneous preterm birth and neonatal morbidity in asymptomatic singleton pregnancies with a short cervix, regardless of prior preterm birth history. Typical regimens include vaginal progesterone gel (90 mg daily) or micronized progesterone capsules (200 mg daily), initiated after diagnosis and continued until approximately 34–36 weeks’ gestation.

The patient should be counseled that progesterone reduces—but does not eliminate—risk, and that adherence is important.

  1. Role of cerclage
    Cervical cerclage is not indicatedin this patient.

High-quality evidence shows no benefit of cerclage in women without a prior spontaneous preterm birth when the indication is ultrasound-detected cervical shortening alone. Cerclage is reserved for a narrowly defined subgroup: singleton pregnancies with both a prior spontaneous preterm birth and a short cervix.

Offering cerclage in this scenario would expose the patient to procedural risks without proven benefit.

Key learning points

  • Asymptomatic cervical shortening is clinically meaningful even in low-risk primigravidas.
  • Vaginal progesterone is the first-line preventive therapy for singleton pregnancies with a short cervix.
  • Cervical cerclage should not be used indiscriminately based on cervical length alone.
  • Clear counseling is essential to reduce anxiety and set realistic expectations.

Case description

A 34-year-old woman, G3P1, presents for routine follow-up at 19+6 weeks’ gestation. Her obstetric history is notable for a previous spontaneous preterm birth at 32 weeks, following spontaneous onset of labor. Her intervening pregnancy ended in a first-trimester miscarriage. She has no history of cervical surgery.

She is currently asymptomatic. Transvaginal ultrasound performed as part of targeted surveillance shows:

  • Cervical length: 22 mm
  • Mild funneling at the internal os
  • Closed external os

She asks whether progesterone is sufficient or whether a surgical intervention should be considered.

Questions raised by the case

  1. How does prior spontaneous preterm birth modify the significance of the cervical length finding?
  2. What preventive strategies are supported by evidence in this scenario?
  3. Is cervical cerclage indicated, and how does it compare with progesterone?

Detailed answer and reasoning

  1. Risk interpretation in the context of prior preterm birth
    This patient combines two major risk factorsfor recurrent spontaneous preterm birth:
  • A history of spontaneous preterm birth, and
  • A short cervix (22 mm) detected in the mid-trimester.

Evidence from cohort studies shows that women with both factors represent the highest-risk subgroup for recurrent preterm delivery. Cervical shortening in this context is not merely a marker but strongly predicts recurrence, particularly at early gestational ages.

  1. Evidence-based preventive strategies
    Two evidence-based strategies must be considered: vaginal progesteroneand cervical cerclage.
  • Vaginal progesterone has proven efficacy in women with a short cervix regardless of obstetric history and remains an appropriate therapy.
  • However, in women with prior spontaneous preterm birth plus a short cervix, additional benefit from cerclage has been demonstrated in randomized trials and meta-analyses.

Thus, progesterone alone may be insufficient in this highest-risk subgroup.

  1. Role of cervical cerclage
    In this specific clinical scenario, cervical cerclage is indicated.

Randomized trials show that, among women with a singleton pregnancy, prior spontaneous preterm birth, and a cervical length typically ≤25 mm before 24 weeks, cerclage reduces recurrent preterm birth and improves neonatal outcomes. The presence of funneling further supports the diagnosis of significant cervical remodeling.

Cerclage is generally performed soon after diagnosis, often between 16 and 24 weeks, and is commonly combined with ongoing progesterone therapy.

Key learning points

  • The combination of prior spontaneous preterm birth and short cervix defines the highest-risk group for recurrence.
  • In this subgroup, cerclage provides benefit beyond progesterone alone.
  • Management must be individualized based on obstetric history and cervical findings.
  • Timing is critical: cerclage is effective only when placed early, before advanced dilation or symptoms.

Case description

A 31-year-old woman, G2P0, presents to the obstetric triage unit at 26+2 weeks’ gestation with regular uterine contractions occurring every 8–10 minutes over the past 6 hours. She has no history of prior preterm birth, cervical surgery, or uterine anomalies.

On examination:

  • No rupture of membranes
  • No vaginal bleeding
  • Digital cervical examination: cervix posterior, approximately 1 cm dilated

Transvaginal ultrasound performed after stabilization shows:

  • Cervical length: 14 mm
  • Prominent funneling
  • Closed external os

She receives intravenous tocolysis with resolution of contractions within 24 hours. Before discharge, the question arises whether repeat cervical length measurement and/or initiation of preventive therapy would alter her prognosis.

Questions raised by the case

  1. What is the prognostic significance of the cervical length in this symptomatic patient?
  2. Does repeating cervical length measurement after successful tocolysis improve risk prediction?
  3. Should vaginal progesterone or cerclage be initiated at this stage?

Detailed answer and reasoning

  1. Prognostic significance of cervical length in symptomatic women
    In the setting of threatened preterm labor, a very short cervical length (14 mm) is associated with a high risk of subsequent preterm delivery, even if contractions resolve temporarily. Cervical length in this context reflects advanced cervical remodeling rather than transient uterine activity alone.

However, it is important to distinguish risk prediction from therapeutic opportunity. At 26+2 weeks, the cervix is already markedly shortened, and the pregnancy is beyond the gestational age window in which most preventive interventions have been shown to be effective.

  1. Value of repeat cervical length after tocolysis
    Repeating cervical length measurement after successful tocolysis is not expected to add meaningful prognostic information.

Evidence indicates that once a short cervix is identified at presentation, short-term changes in cervical length over the subsequent 24–48 hours do not significantly improve prediction of preterm birth beyond the baseline measurement. Apparent lengthening or further shortening may reflect transient physiological or technical variation rather than true biological progression.

Therefore, a repeat scan before discharge should not be used to guide major management decisions.

  1. Role of progesterone and cerclage at this stage
  • Vaginal progesterone:
    Progesterone has proven benefit when initiated in asymptomatic women with a short cervix between 16 and 24 weeks. Evidence for starting progesterone after 24–25 weeks in symptomatic women is limited, and benefit is uncertain. While some clinicians may still consider progesterone due to its safety profile, it should not be presented as a clearly evidence-based intervention in this context.
  • Cervical cerclage:
    Cerclage is contraindicated in this scenario. The patient is symptomatic, beyond the optimal gestational age window, and has evidence of cervical change. Placement of cerclage at this stage carries significant risk (infection, rupture of membranes) without demonstrated benefit.

Management should instead focus on short-term pregnancy prolongation (e.g. corticosteroids for fetal lung maturation, magnesium sulfate for neuroprotection if appropriate) and planning for potential preterm delivery.

Key learning points

  • In threatened preterm labor, a very short cervix indicates high risk but limited preventive options.
  • Baseline cervical length is prognostically important; repeat measurements after tocolysis are not.
  • Progesterone is most effective when started early and in asymptomatic women.
  • Cerclage should not be used in symptomatic patients or late in gestation.
  • Management priorities shift from prevention to mitigation of neonatal risk.

Case description

A 30-year-old woman, G2P1, is seen at 22+3 weeks’ gestation for routine antenatal care. Her obstetric history includes a term vaginal delivery without complications. She has no history of cervical surgery, uterine anomalies, or preterm labor.

This pregnancy is a dichorionic diamniotic twin pregnancy, conceived spontaneously. She is asymptomatic. Because of the twin gestation, transvaginal ultrasound cervical assessment is performed and shows:

  • Cervical length: 23 mm
  • No cervical funneling
  • Closed internal and external os

She asks whether treatment is needed to reduce the risk of preterm birth.

Questions raised by the case

  1. How should cervical length be interpreted in twin pregnancies?
  2. Does a cervical length of 23 mm warrant intervention in this context?
  3. What preventive strategies, if any, are supported by evidence? 

Detailed answer and reasoning

  1. Interpretation of cervical length in twin pregnancies
    Twin pregnancies have a higher baseline risk of spontaneous preterm birth, largely due to uterine overdistension and altered cervical biomechanics. Cervical shortening is common, and median cervical length values are typically lower than in singleton pregnancies at comparable gestational ages.

While a cervical length of 23 mm would be considered abnormal in a singleton pregnancy, its predictive value in twins is weaker, and the positive predictive value for early spontaneous preterm birth is substantially lower. Importantly, cervical length in twins remains a risk marker, but its presence does not automatically identify a population in which intervention is effective.

  1. Should intervention be initiated?
    Despite the presence of a “short” cervix by singleton standards, routine intervention is not recommendedin this scenario.

High-quality randomized trials and meta-analyses have consistently shown that:

  • Vaginal progesterone does not reliably reduce preterm birth in unselected twin pregnancies with a short cervix.
  • Cervical cerclage in twins with a short cervix provides no benefit and may increase adverse outcomes, including earlier delivery.

Therefore, a cervical length of 23 mm at 22 weeks in an asymptomatic twin pregnancy does not justify intervention based on current evidence.

  1. Evidence-based management strategy
    Management should focus on:
  • Expectant management, with careful clinical follow-up
  • Patient counseling, emphasizing the limitations of available preventive strategies
  • Avoidance of interventions with no proven benefit (progesterone, cerclage, bed rest)

Some clinicians may consider increased surveillance, but routine serial cervical length measurements should be approached cautiously, as they may increase anxiety without changing management.

Key learning points

  • Cervical length thresholds derived from singleton pregnancies cannot be directly extrapolated to twins.
  • In twin pregnancies, cervical shortening predicts risk but does not identify a group that clearly benefits from intervention.
  • Progesterone and cerclage are not routinely recommended for asymptomatic twin pregnancies with a short cervix.
  • Counseling should emphasize evidence-based care and avoid false reassurance or unnecessary intervention.

Case description

A 36-year-old woman, G4P1, presents at 18+5 weeks’ gestation for targeted cervical surveillance. Her obstetric history includes:

  • One spontaneous preterm birth at 29 weeks, complicated by neonatal respiratory distress
  • One second-trimester pregnancy loss at 20 weeks, attributed retrospectively to painless cervical dilation
  • One term delivery after close monitoring

She has a history of a cone biopsy performed 6 years earlier for CIN 3. She is currently asymptomatic.

Transvaginal ultrasound shows:

  • Cervical length: 26 mm
  • Progressive U-shaped funneling involving approximately 30% of the cervical canal
  • Closed external os

She asks whether intervention is necessary given that her cervical length is “just above normal.”

Questions raised by the case

  1. How should cervical length be interpreted in the presence of funneling and a high-risk history?
  2. Does a cervical length slightly above 25 mm exclude significant risk?
  3. What is the most appropriate management strategy?

Detailed answer and reasoning

  1. Risk interpretation in a high-risk patient
    This patient represents a very high-risk profiledue to the combination of:
  • Prior early spontaneous preterm birth,
  • A second-trimester loss consistent with cervical insufficiency, and
  • Prior cervical surgery (cone biopsy).

Although the measured cervical length is 26 mm, which lies just above the commonly used threshold, this must be interpreted in context. Cervical length should never be interpreted in isolation. The presence of progressive funneling, particularly U-shaped funneling, suggests active cervical remodeling and loss of internal os competence.

In high-risk women, risk stratification relies on the interaction between history and cervical morphology, not on a single numeric cutoff.

  1. Limitations of strict cervical length thresholds
    This case illustrates why cervical length thresholds (e.g. 25 mm) are pragmatic rather than biological. A cervix measuring 26 mm with significant funneling in a woman with prior early preterm birth does notrepresent reassurance.

Evidence indicates that:

  • Cervical funneling reflects early internal os opening and structural weakness.
  • In women with a strong history of cervical insufficiency, funneling may precede rapid shortening.
  • Small measurement differences (1–2 mm) fall well within technical variability.

Therefore, the patient’s risk remains substantial, despite the numerical value.

  1. Evidence-based management strategy
    In this scenario, cervical cerclage is indicated, even though cervical length is slightly above 25 mm.

Guidelines and trial data support cerclage in women with:

  • Singleton pregnancy
  • Prior spontaneous preterm birth or second-trimester loss
  • Evidence of cervical change (shortening and/or funneling) before 24 weeks

Given the patient’s history and ultrasound findings, cerclage offers the best chance of reducing recurrent early preterm birth. Cerclage should be placed promptly, typically before 20–22 weeks if possible.

Adjunctive vaginal progesterone may also be used, although evidence for additive benefit is less robust; many clinicians combine therapies in very high-risk patients.

Key learning points

  • Cervical length thresholds are context-dependent and must be interpreted alongside history and morphology.
  • Cervical funneling is a marker of structural cervical failure, especially in high-risk women.
  • In women with prior early preterm birth and suggestive ultrasound findings, cerclage may be justified even when length is borderline.
  • Overreliance on numeric cutoffs risks missing evolving cervical insufficiency.

Case description

A 28-year-old woman, G1P0, is referred at 20+1 weeks’ gestation after an incidental finding of a short cervix during a routine fetal anatomy scan. She has no medical comorbidities, no prior cervical procedures, and no family history of preterm birth. She is completely asymptomatic.

Transvaginal ultrasound performed by an experienced operator shows:

  • Cervical length: 24 mm
  • No funneling
  • Internal and external os closed
  • Adequate image quality with minimal probe pressure

She is concerned because the cervical length is “below normal” and asks whether this means she will deliver prematurely and whether aggressive treatment is required.

Questions raised by the case

  1. How should a cervical length of 24 mm be interpreted in a low-risk primigravida?
  2. Does this finding justify intervention, and if so, which one?
  3. How should counseling and follow-up be organized?

 

Detailed answer and reasoning

  1. Interpretation of cervical length in this context
    A cervical length of 24 mm at 20 weekslies just below the commonly used threshold of 25 mm. In a low-risk primigravida, this finding indicates a moderately increased riskof spontaneous preterm birth, but it does not imply imminent cervical failure or inevitability of early delivery.

It is essential to emphasize that cervical length represents a continuous risk variable. The absolute risk associated with a length of 24 mm is substantially lower than that associated with more severe shortening (e.g. <15–20 mm), particularly in the absence of prior preterm birth or cervical surgery.

  1. Evidence-based intervention
    Despite the modest degree of shortening, vaginal progesterone is indicated.

Randomized trials have demonstrated that vaginal progesterone reduces spontaneous preterm birth in asymptomatic singleton pregnancies with cervical length ≤25 mm, regardless of obstetric history. Importantly, benefit has been shown across a range of cervical lengths below this threshold, not only in extreme shortening.

By contrast:

  • Cervical cerclage is not indicated, as there is no prior preterm birth or evidence of cervical insufficiency.
  • Bed rest, activity restriction, or prophylactic tocolysis are not supported by evidence and should be avoided.
  1. Counseling and follow-up strategy
    Counseling should be reassuring but honest:
  • Explain that the risk is increased but most women with this finding will still deliver at term.
  • Emphasize that progesterone is a preventive, low-risk intervention that significantly reduces the chance of early preterm birth.

Follow-up typically includes:

  • Initiation of daily vaginal progesterone
  • Consideration of repeat cervical length measurement in 1–2 weeks to ensure stability, although routine serial scans should be limited to situations where results would alter management. 

Key learning points

  • Mild cervical shortening in low-risk women still has clinical significance.
  • Vaginal progesterone is appropriate even when cervical length is only slightly below threshold.
  • Cerclage should not be used without a strong historical or structural indication.
  • Patient counseling should focus on risk reduction, not determinism.

Case description

A 35-year-old woman, G3P2, presents at 21+6 weeks’ gestation for evaluation after a routine ultrasound identified cervical shortening. Her obstetric history includes:

  • Two term vaginal deliveries without complications.
  • No history of preterm birth or second-trimester loss.

However, her gynecologic history is notable for a large loop excision of the transformation zone (LLETZ) performed 4 years earlier for high-grade cervical dysplasia.

She is asymptomatic. Transvaginal ultrasound shows:

  • Cervical length: 19 mm
  • No funneling
  • Closed internal and external os

She asks whether her prior cervical surgery changes management and whether cerclage is required.

Questions raised by the case

  1. How does prior cervical excisional surgery influence interpretation of cervical length?
  2. What is the most appropriate evidence-based intervention?
  3. Is cervical cerclage indicated solely based on prior cervical surgery?

Detailed answer and reasoning

  1. Impact of prior cervical surgery on cervical length interpretation
    Excisional cervical procedures such as LLETZ or cone biopsy are associated with an increased risk of spontaneous preterm birth, primarily due to reduction in cervical tissue volume and potential disruption of cervical integrity. Women with prior cervical surgery often have shorter baseline cervical lengths, even in pregnancies that ultimately reach term.

However, prior cervical surgery alone does not equate to cervical insufficiency. The key question is whether the observed shortening represents functional cervical failure or a stable anatomical consequence of surgery.

In this case, a cervical length of 19 mm at 21–22 weeks represents true shortening, not merely a borderline finding, and confers a significantly increased risk of spontaneous preterm birth—even in the absence of prior preterm delivery.

  1. Evidence-based management
    The most appropriate intervention is vaginal progesterone.

Randomized trials have demonstrated that vaginal progesterone reduces preterm birth in asymptomatic singleton pregnancies with a short cervix, regardless of obstetric history or etiology of shortening. Prior cervical surgery does not diminish progesterone efficacy.

Progesterone should therefore be initiated promptly and continued until approximately 34–36 weeks’ gestation.

  1. Role of cervical cerclage
    Cervical cerclage is not indicatedin this patient.

Evidence does not support cerclage based solely on:

  • Prior cervical excisional surgery, or
  • Ultrasound-detected short cervix in the absence of prior spontaneous preterm birth.

Cerclage is reserved for women with a documented history of spontaneous preterm birth or second-trimester loss, combined with cervical shortening in the current pregnancy. Using cerclage in this scenario would expose the patient to procedural risks without proven benefit.

Key learning points

  • Prior cervical surgery increases baseline risk but does not automatically justify cerclage.
  • Cervical length remains the primary determinant of current pregnancy risk.
  • Vaginal progesterone is first-line therapy for asymptomatic short cervix, regardless of etiology.
  • Cerclage should not be used indiscriminately in women without prior preterm birth.

Case description

A 32-year-old woman, G2P1, is evaluated at 23+1 weeks’ gestation after referral for suspected cervical shortening. Her obstetric history includes:

  • One term vaginal delivery.
  • No history of preterm birth or second-trimester loss.

She is asymptomatic. Her current pregnancy is a singleton. Transvaginal ultrasound performed by two experienced operators shows:

  • Cervical length: 15 mm.
  • Marked V-shaped funneling extending to the mid-cervix.
  • Closed external os.

A repeat scan 48 hours later confirms similar findings. She asks whether immediate surgical treatment is required given the degree of shortening.

Questions raised by the case

  1. How should a very short cervix (15 mm) with funneling be interpreted in a woman without prior preterm birth?
  2. Does the severity of shortening alone justify cervical cerclage?
  3. What is the optimal evidence-based management strategy at this gestational age?

Detailed answer and reasoning

  1. Risk interpretation
    A cervical length of 15 mm at 23 weeksrepresents severe cervical shorteningand is associated with a substantially increased risk of early spontaneous preterm birth, even in women without prior preterm delivery. The presence of marked funneling indicates advanced internal os remodeling and reinforces the high-risk nature of this finding.

However, risk magnitude does not automatically determine intervention choice. Management must still be guided by evidence of benefit, not solely by perceived severity.

  1. Role of cervical cerclage in the absence of prior preterm birth
    Despite the dramatic ultrasound appearance, cervical cerclage is not routinely indicatedin this scenario.

Randomized trials evaluating cerclage for ultrasound-detected short cervix have consistently shown no benefit in women without a prior spontaneous preterm birth, even when cervical length is very short. The apparent severity of shortening does not override the lack of demonstrated efficacy and exposes the patient to procedural risks, including infection and preterm premature rupture of membranes.

Emergency or “rescue” cerclage is also not appropriate here, as the patient is asymptomatic, has a closed external os, and lacks a history suggestive of classic cervical insufficiency.

  1. Evidence-based management strategy
    The optimal management is vaginal progesterone therapy.

High-quality randomized trials demonstrate that vaginal progesterone significantly reduces early preterm birth in asymptomatic singleton pregnancies with cervical length ≤15–20 mm, regardless of obstetric history. Treatment should be initiated immediately and continued until approximately 34–36 weeks’ gestation.

Adjunctive measures include:

  • Careful counseling regarding signs of preterm labor
  • Avoidance of ineffective interventions (bed rest, prophylactic cerclage)
  • Judicious follow-up, with repeat cervical length measurement only if results would alter management

 Key learning points

  • Severity of cervical shortening increases risk but does not expand cerclage indications.
  • Evidence supports vaginal progesterone as first-line therapy even in very short cervix without prior preterm birth.
  • Funneling alone does not justify cerclage in low-history patients.
  • Management decisions must remain evidence-based, not reactionary.

Case description

A 27-year-old woman, G2P0, presents at 22+0 weeks’ gestation after referral for cervical assessment. Her obstetric history includes:

  • One second-trimester pregnancy loss at 21 weeks, described as painless cervical dilation followed by rapid delivery
  • No history of uterine contractions, infection, or placental pathology during that loss

She has no history of cervical surgery. In the current pregnancy, she is asymptomatic.

Transvaginal ultrasound shows:

  • Cervical length: 28 mm
  • Progressive Y-shaped funneling at the internal os
  • External os closed

Speculum examination confirms a closed cervix with no visible membranes. The referring physician questions whether intervention is justified given the “normal” cervical length.

Questions raised by the case

  1. How should this obstetric history influence interpretation of the current ultrasound findings?
  2. Does a cervical length of 28 mm exclude cervical insufficiency?
  3. What is the most appropriate evidence-based management strategy?

Detailed answer and reasoning

  1. Importance of obstetric history
    This patient’s prior pregnancy loss at 21 weeks, characterized by painless cervical dilation and rapid expulsion, is highly suggestive of cervical insufficiency. In such cases, obstetric history carries greater diagnostic weight than cervical length alone.

Cervical insufficiency is a clinical diagnosis, traditionally defined by recurrent painless mid-trimester losses or early preterm births associated with cervical dilation in the absence of contractions or infection. Ultrasound findings in the subsequent pregnancy may be subtle or even normal early in the disease course.

  1. Limitations of relying on cervical length alone
    A cervical length of 28 mmwould generally be reassuring in a low-risk woman. However, in this context, it does not exclude significant cervical pathology.

Key points include:

  • Cervical insufficiency may initially present with internal os funneling before measurable shortening.
  • Funneling reflects loss of internal os competence and may precede rapid, unpredictable cervical change.
  • Cervical length measurement captures geometry, not structural integrity.

Therefore, the combination of a highly suggestive obstetric history and evolving funneling outweighs the apparently normal length.

  1. Evidence-based management strategy
    The most appropriate management is prophylactic (history-indicated) cervical cerclage.

Guidelines and clinical evidence support cerclage placement in women with:

  • A history of one or more second-trimester losses consistent with cervical insufficiency,
  • Even when cervical length in the current pregnancy is normal or near normal.

In this scenario, waiting for cervical shortening would risk sudden, irreversible cervical dilation. Cerclage should be placed promptly, typically between 12 and 14 weeks, but at 22 weeks it may still be considered if the cervix is closed and there is no infection or labor.

Adjunctive vaginal progesterone may be considered, although evidence for additive benefit in classic cervical insufficiency is limited.

Key learning points

  • Cervical insufficiency is primarily a historical diagnosis, not an ultrasound diagnosis alone.
  • Normal or near-normal cervical length does not exclude risk in women with classic prior losses.
  • Cervical funneling may precede measurable shortening.
  • History-indicated cerclage is justified even when cervical length is not shortened.

Case description

A 33-year-old woman, G2P1, is referred at 24+0 weeks’ gestation because of concern about progressive cervical change. Her obstetric history includes:

  • One term vaginal delivery without complications
  • No history of preterm birth or second-trimester loss

She is asymptomatic, with no uterine contractions, vaginal bleeding, or rupture of membranes. Her current pregnancy is a singleton.

Cervical assessment shows:

  • Transvaginal ultrasound cervical length: 17 mm
  • Moderate funneling of the internal os
  • External os closed

She was not screened earlier in pregnancy. The referring clinician asks whether late intervention could still reduce the risk of preterm birth.

Questions raised by the case

  1. How should cervical shortening detected at the upper limit of the screening window be interpreted?
  2. Are preventive interventions still effective at 24 weeks?
  3. What management strategy is supported by evidence at this gestational age?

Detailed answer and reasoning

  1. Interpretation of cervical shortening at 24 weeks
    A cervical length of 17 mm at 24 weeksrepresents significant cervical shortening and is associated with an increased risk of spontaneous preterm birth. However, this finding occurs at the upper boundary of the validated screening window.

At this gestational age, cervical shortening may reflect:

  • Ongoing but potentially modifiable cervical remodeling, or
  • A more advanced stage of the preterm parturition process, with limited opportunity for prevention.

Thus, risk remains substantial, but the window for effective intervention is narrowing.

  1. Effectiveness of preventive interventions at this stage
  • Vaginal progesterone:
    Evidence for vaginal progesterone is strongest when initiated between 16 and 24 weeks. Although most randomized trials enrolled women before 24 weeks, initiation at 24 weeks is still considered reasonable and biologically plausible, particularly in asymptomatic women. Given its excellent safety profile, progesterone remains the only evidence-supported preventive option in this scenario.
  • Cervical cerclage:
    Cerclage is not indicated. The patient has no prior spontaneous preterm birth, and placement at 24 weeks carries increased procedural risk with no proven benefit in this population.
  • Other interventions:
    Bed rest, activity restriction, and prophylactic tocolysis have no evidence of benefit and should be avoided.
  1. Evidence-based management strategy
    The most appropriate management is:
  • Immediate initiation of vaginal progesterone
  • Careful counseling regarding signs of preterm labor
  • Consideration of follow-up cervical assessment only if results would alter care

At this gestational age, management should also include anticipatory planning, recognizing that prevention may be incomplete. If further shortening or symptoms develop, focus should shift toward timely antenatal corticosteroids and perinatal planning rather than late preventive interventions.

Key learning points

  • Cervical shortening detected at 24 weeks still conveys increased risk but offers limited preventive opportunity.
  • Vaginal progesterone remains appropriate at the upper boundary of the screening window.
  • Cerclage should not be introduced late or without historical indication.
  • Early screening is crucial to maximize the benefit of preventive strategies.
Revision sheet

  1. Core definitions (must know)

 Preterm birth (PTB)

Delivery before 37 completed weeks of gestation.

Spontaneous preterm birth (sPTB)

Preterm delivery following spontaneous labor or PPROM, not medically indicated.

Cervical length (CL)

Distance between the internal and external os, measured by transvaginal ultrasound (TVUS).

Short cervix

Usually defined as ≤25 mm in the mid-trimester (16–24 weeks).
➡️ This is a pragmatic threshold, not a biological cutoff.

Cervical insufficiency

Clinical diagnosis characterized by painless cervical dilation leading to recurrent mid-trimester loss or early preterm birth, often diagnosed by history, not ultrasound alone.

 

  1. Key pathophysiological concepts

  • sPTB is a final common pathway of multiple processes (infection, inflammation, ischemia, mechanical factors).
  • Cervical remodeling involves:
    • Softening (biochemical)
    • Shortening (geometric)
    • Dilation (structural failure)
  • Cervical shortening is often a marker, not the primary cause.

 

  1. Cervical length as a predictor

Fundamental principles

  • Risk of sPTB increases continuously as cervical length shortens.
  • Predictive value is strongest between 16–24 weeks.
  • Most early sPTBs occur in women without prior preterm birth.

High-risk combinations

  • Prior sPTB + short cervix → highest recurrence risk.
  • Short cervix alone is still clinically meaningful.

 

  1. How to measure cervical length (exam favorite)

 Gold standard

✅ Transvaginal ultrasound (TVUS)

Technical essentials

  • Empty bladder
  • Minimal probe pressure
  • Clear visualization of internal and external os
  • Use the shortest correct measurement

What NOT to rely on

❌ Digital examination (subjective, poor prediction)
❌ Transabdominal ultrasound for screening

 

  1. Interpretation pearls

  • Cervical length is a risk marker, not destiny.
  • Small differences (e.g. 24 vs 26 mm) may be within measurement variability.
  • Funneling suggests internal os weakness but does not replace CL.
  • Always interpret CL in clinical context (history, gestational age).

 

  1. Evidence-based interventions

 Vaginal progesterone (FIRST LINE)

Indication

  • Asymptomatic singleton pregnancy
  • Cervical length ≤25 mm
  • With or without prior sPTB

Effect

  • ↓ Early sPTB (<33–34 weeks) by ~40–45%
  • ↓ Neonatal morbidity

Practical

  • Vaginal gel (90 mg) or capsules (200 mg)
  • Start when detected, continue to 34–36 weeks

Cervical cerclage (SELECTIVE)

Indicated when

  • Singleton pregnancy
  • Prior spontaneous preterm birth or second-trimester loss
  • Short cervix detected before 24 weeks

NOT indicated

  • Short cervix alone without prior sPTB
  • Twin pregnancies
  • Symptomatic women or late gestation

 

  1. Special situations

 Twin pregnancies

  • CL predicts risk but interventions do not work the same
  • Progesterone and cerclage → no routine benefit
  • Do NOT extrapolate singleton data

Threatened preterm labor

  • Admission CL predicts risk
  • Repeat CL after tocolysis adds no value
  • Prevention window often already passed

Prior cervical surgery

  • Increases baseline risk
  • Management depends on current CL + obstetric history
  • Surgery alone ≠ indication for cerclage

 

  1. Emerging tools (know the concept)

 Cervical elastography

  • Measures cervical stiffness
  • Softer cervix associated with sPTB
  • Currently investigational
  • Does NOT replace cervical length

 

  1. Common exam traps & pitfalls

❌ Treating all short cervixes with cerclage
❌ Assuming normal CL excludes risk in classic cervical insufficiency
❌ Applying singleton evidence to twins
❌ Overinterpreting short-term CL changes
❌ Recommending bed rest (no benefit, potential harm)

 

  1. Take-home exam summary

  • TVUS cervical length (16–24 weeks) = best predictor of sPTB
  • Vaginal progesterone = first-line prevention for short cervix in singletons
  • Cerclage = only for selected high-risk women
  • Screening is only useful if actionable
  • Prevention works best before symptoms appear
Quiz

Ce Quiz comporte 10 QRM
Chaque question a une seule réponse exacte
Un minimum de 80% de réponses exactes est requis
Le temps imparti est de 5 mn au maximum

Le temps imparti est écoulé

Mesure de la longueur du col

1 / 10

Best overall summary statement:

2 / 10

In twin pregnancies, cervical length:

3 / 10

In singleton pregnancies, first-line therapy for asymptomatic short cervix is:

4 / 10

The primary mechanism of action of progesterone in preventing preterm birth includes:

5 / 10

Cervical cerclage acts mainly by:

6 / 10

Vaginal progesterone has been shown to reduce preterm birth in:

7 / 10

Progesterone treatment should usually be continued until:

8 / 10

Digital cervical examination is inferior to TVUS because it is:

9 / 10

Universal cervical length screening is supported because:

10 / 10

Current role of cervical elastography in practice:

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